1. Field of the Invention
The present invention generally relates to methods and apparatus for automatically making periodic quantitative determinations of bacteria present in water. More particularly, the invention relates to method and apparatus for automatically making periodic quantitative determinations of coliform organisms present in water such as waste water, effluent or fresh water by using electrochemical techniques based on detection of metabolic hydrogen liberated by the coliform organisms utilizing changes in electrode potentials.
2. Description of the Prior Art
Detection and quantitative measurement of the number of coliform bacteria present in water is frequently of vital importance for determining the effectiveness of water treatment processes in removing bacterial contamination. The predominance in sewage of coliform bacteria make this organism a sensitive indicator of pollution. Water is an unfavorable environment for bacteria and those that find their way into water gradually die off. Coliform, along with other bacteria, are also quite readily removed from water by conventional water purification processes. The common intestinal bacteria pathogens are at least as susceptible to the artificial and natural purification processes to which water is subjected as is a more common coliform bacteria. Therefore, the coliform group may be employed as a good indicator of pollution.
Presently, several methods are known for the detection of coliform bacteria in aqueous solutions. These methods are generally divided into two classes of detection, both being based on the production of metabolic hydrogen liberated by the coliform organisms after innoculation into a lactose-containing nutrient broth. However, the prior art techniques developed heretofore are generally time consuming and complex since the techniques involve laboratory procedures which require continual intervention by trained personnel.
One such technique for the quantitative determination of coliform bacteria in an aqueous sample is to position the culture to be tested inside a hermetically sealed chamber and thereafter to measure the increase in pressure due to the metabolically produced hydrogen. For example, Wilkins et al, U.S. Pat. No. 3,907,646, utilizes a differential pressure transducer fitted to a metal cap machined to hermetically seal a conventional test tube. The inlet tube of the transducer is inserted through the cap and soldered into place. The culture to be tested is positioned inside the test tube and the tube and transducer assembly placed within the incubator with the electric output of the transducer being connected to a measuring device. As hydrogen is evolved during the growth cycle of the coliform bacteria, the pressure on the interior of the test tube increases, resulting in a measurable output from the pressure transducer.
The second technique is directed to measuring an increase in voltage in the negative (cathodic) direction resulting from the metabolically induced hydrogen. The increase in electrical potential is measured by a system utilizing two electrodes. For example, Wilkins et al, U.S. Pat. No. 4,009,078, utilizes a test tube containing two electrodes positioned in a growth nutrient broth containing coliform organisms, which is then positioned in a 35.degree. C. water bath. Hydrogen evolution was measured by an increase in voltage in a negative direction caused by metabolic hydrogen production induced by the growth of the bacteria in the culture. As the induced hydrogen increased, the potential difference increased, and with the outputs of the electrodes connected to a suitable measuring device, the increase in potential difference becomes measurable.
Both of the above-described coliform bacteria detection methods utilize a laboratory test tube as the culture cell. While these laboratory methods provide for a rapid determination that bacteria are present in an aqueous sample, they still require constant supervision and intervention by trained personnel to perform the test and are time consuming.
The present invention overcome the deficiencies of the prior art by providing methods and apparatus for automatically and periodically measuring the concentration of coliform bacteria present in a given sample by apparatus which is interfaced with, and controlled by a digital computer enabling the apparatus to provide the desired concentration measurement on a periodic or continuous basis.